Fragmentation of the Southern Brown Bandicoot Isoodon obesulus: Unraveling Past Climate Change from Vegetation Clearing

Distribution modeling and vegetation suitability mapping were undertaken to assess (1) the role that past climate change played in fragmenting a subspecies of the endangered southern brown bandicoot Isoodon obesulus and (2) the impacts of land cover change on the subspecies following European settlement of Australia. Based on a selection of bioclimatic variables, disjunctions in the broad distribution of I. obesulus obesulus were found. Vegetation maps representing the time of European settlement revealed two clear features. First, vegetation that was unsuitable for the subspecies corresponded to climatic disjunctions in its distribution, and, second, substantial additional areas were predicted to have suitable vegetation but not suitable climate. Vegetation mapping showed considerable change over two centuries after European settlement, so that most places that formerly had suitable climate and vegetation were cleared. Our analysis demonstrates that clearing of native vegetation has masked naturally occurring disjunctions in the distribution of I. o. obesulus. This finding provides evidence that fragmented, regional-scale populations of I. o. obesulus existed prior to European settlement. Implications for conservation planning are discussed. 1. Introduction Fragmentation has been variously described as either naturally occurring or anthropogenic disruption to habitat continuity that can operate across multiple spatial, temporal, and functional domains [1–3]. Most fragmentation studies focus on the patch scale and biotic effects of relatively recent anthropogenic impacts, for example, loss of habitat through vegetation clearing, increased isolation of remnants, and exposure to edge effects [4–7]. But fragmentation can be considered at much broader spatial and temporal scales including global-scale vicariance events, such as continental drift in the Paleocene-Pliocene, or regional-scale disruption to species distributions during the Pleistocene and Holocene. For example, marsupial evolution and radiation in Australia and South America are largely understood in the context of the continents’ long-term isolation following separation from Gondwana [8], and at a different, finer scale, the distribution of oligostenothermic species such as the mountain pygmy-possum Burramys parvus in south-eastern Australia has been fragmented by the change to the thermocline after the last glacial maximum [9]. Scale is a key issue in the present study in which we examine how natural and anthropogenic factors have interacted to fragment the distribution of an endangered